Docker

What is Docker?

• Docker is a standard for Linux containers
• A "Container" is an isolated runtime inside of Linux
• A "Container" provides a private machine like space under Linux
• Containers will run under any modern Linux Kernel

Containers can:

• Have their own process space
• Their own network interface
• 'Run' processes as root from inside the container
• Have their own disk space
  • Can also share with Host

Docker Terminology

• Docker Image - The representation of a Docker Container.
• Docker Container - The standard runtime of Docker
• Docker Engine - The code which manages Docker stuff

Docker Editions

Docker Community Edition

• CaaS (Contianer as a Service platform subscription)
• Quarterly Releases
• Enterprise Class Support

Docker Enterprise Edition

• Free for developers and operations
• Monthly 'edge' release for devs and quartly releases for operations

Docker uses the release number of year.month.version.edition (yy.mm.v.ed)

Docker Images

• Images are immutable
• Images are built in layers
  • Each layer is an immutable file, but is a collection of files and directories
  • Layers recive an ID calculated via a SHA 256 hash of the layer contents
    • So if layer contents change at all, the SHA 256 hash changes also
• Running docker images gives the first 12 characters of the hash in 'Image ID'
• The hash values of images are referred to by 'tag' names
• The format of the full tag name is: [REGISTRYHOST/][USERNAME/]NAME[:TAG]
  • For Registry Host 'registry.hub.docker.com' is inferred
  • For ':TAG' - 'latest' is default and inferred
  • Full tag example: 'registry.hub.docker.com/mongo:latest'
• Old volumes and containers can pile up and use up disk space, cleanup is important